Protective arrangement for sectionalized electric power circuits



June 24, 1930. w, sco ET! AL 1,765,887

PROTECTIVE ARRANGEMENT FOR sEcTIoNALIzEDELEcTRIc POWER CIRCUITS Filed Feb. 2'7, 1929 4 Sheets-Sheet 1 Hal June 24, 1930.. E. w. M. SCOTT ET AL 1,765,887

. PROTECTIVE ARRANGEMENT FOR SECTIONALIZED EIAECTRIC POWER CIRCUITS Filed Feb. 27, 1929. 4 Sheets-Sheet 2 Jqne 24 1930. E. w. M. SCOTT ET AL. 1,765,887

PROTECTIVE ARRANGEMENT FOR SECTIONALIZED ELECTRIC POWER CIRCUITS Filed Feb. 2'7, 1929 4 Sheets-Sheet I:

jaw MVM g.

June 24, 1930.

E. W. M. SCOTT AL PROTECTIVE ARRANGEMENT FOR SECTIONALIZED ELECTRIC POWER CIRCUITS Filed Feb. 27, 1929 4 Sheets-Sheet 4 hatented I June 24, 1&30

' Jam-:1) 'rarase orrica 4 ERIC WALTEB MKBBURY SCOTT, 0F CHURCH STRETTON, BRUCE HAMEIB- LEESON,

0F TYNEMOUTH, ENGLAND; ASSIGNOBS TO A. REYROLLE & COMPANY LmITED, OI"

BUBN-QN-TYHE, ENGLANDQA conrnnr or GREAT BRITAIN raorac'rmn ARRANGEMENT For. sac'i'rorranznn mcrmc rowaacmcurrs Application and llfebruary 27, 1929, Serial to. 348,162, and in Great Britain April 2, 192a.

balanced against that leaving the section at,

the other end. Such arrangements, besides requiring accurate calibration of current transformers and other apparatus, usually entail the use of heavily insulated and expensive pilot wires and necessitate the pro.- vision of relatively complicated compensating apparatus for preventing inadvertent operation of the protective gear as the result for-instance of capacity currents in the pilot circuit more especially in the case of pilot wires of great length.

- The present invention has for its object 25 to provide a protective arrangement for the sections of an electric power clrcuit in which such difliculties and complications are avoided.

In the arrangement according to the in: vention each section is protected-independently of the other sections'by means of a protective arrangement comprising a tripping relay device at each end controlling a tripping circuit for" a circuit-breaker at the adjacent end of the section, a stabilizing relay device at each end operative. on the occurrence a fault in the system only when the current in the power circuit is flowing outfrom the section at the end ad'acent to the stabilizing relay device, an means whereby each stabilizing relay device when operated causes a stabilizing current to be transmitted to the remote end of the section and thereby prevents the circuit-breaker at.

the reinote end from being opened by its ipp'ing relay-device. Y -Each" tri ping:;relay device may be so arbegoperative on the occurrence he ystem only when-the current rcuit is flowing into the section at the end adjacent to the device, but preferably each tripping relay device is operative on the occurrence of a fault irre- *spective of the direction of flow of. current in the protected section. With this arrangement each stabilizing relay device preferably acts to prevent the circuit-breakers at both ends from being opened by their tripping relay devices.

Each stabilizing relay device preferably acts.to connect a local source of current to pilot wires connected at the remote end to a j lock-out relay associated with the tripping relay device at that end. With this arrangement it, will be apparent that the pilot 05 wires-need never be called upon to have greater. voltage applied to them or to carry greater current than is necessary for the operation ofthe lock-out relays, and consequently the difliculties and expense attendant upon the use of the pilot wires required in-Merz-Price systems are avoided. Pref-' erably the pilot wires which carry the stabilizing currents are normally employed for other purposes such as the transmission of telephonic or supervisory control currents. Alternatively pilot wires may .be dispensed with altogether, .the stabilizing eurrents then consisting of or being earned by high frequency currents superimposed on the conductors of the power circuit.

The relay devices may be arranged in various ways. Thus when the invention is applied to a polyphase power circuit, each of the. four relay devices on each section may comprise an overload relay or group of, overload relays and an earth leakage relay, the overload and earth leakage relays acting in parallel to control the tripping or stabilizing circuits either directly or through an auxiliary relay. These relays are directional in operation in the case or the stabilizing relay devices and also in some instances in the case. of the trippingre ay devices. The overload relays may have their current coils energized from current transformers in the -protected section and their voltage coils energized from potential transformers in the section. In the case of a high voltage transmission circuit, where 100 neutral point of the hlgh tension winding of the vower transformer.

The invention may be carried into prac-.

tioe. in various ways but someeconvementractical' arrangements according thereto are illustrated in the accompanying drawings as applied to a sectionalized high tension threephase power transmission line (such as a ring main) wherein the sections extend from station to station-and are capable of being supplied with power from either end. In these drawings, 7

Figures 1 and-2 show one arran ement, Figure 1 showing the protective re ay apparatus at one station, whilst Figure 2 includes art of two adjacent stations and shows t e tri ping and stabilizin circuits concerned wit the protection of t e section between the stations,

Figure 3 shows a modification of the circuits of Figure 2, 1 I

Figure 4 is a diagram similar to that of Figure 1' but illustrating a preferred arran ment,

lgures 5 to 8 show further modifications of the preceding arrangements, Figure 9 illustrates an ap lication of the invention to the protection 0 duplicate feeders, and

Figure 10 shows an extension of the ar-- rangement of Fi re 9 to deal with the case of licate fee ers, one of which is-interrupte atone or more points for supply tov intermediate substations.

In cases where a drawing shows two stations one at each end of the protected section,-

small reference letters are employed for the parts at one station which are similar to'the parts at the other stationindicated by the corresponding capital letters, and in such cases a description will only be given of the parts at one of the stations.

In the arrangement of Figures 1 and 2 the invention is illustrated as applied to the protection of a section A terminating at each end in a duplicate supply substation, of the kind in which the two sections A A adjacent to each substation are connected to-. gether through a main circuit breaker A and are each connectedv through a circuitbreaker A to the primary A- of a power transformer whose secondary A supplies a distribution circuit. Each power'transformer primary A is in this instance star-connected with its neutral point earthed at A.

Each substation is provided with four relay devices, two of which are associatedwith the rotection of thesection A under consid'-- aving current coils B and volta e coils B and an earth leaka e directiona relay B havin a current coil B and what will be terme a voltage coil B in accordance with-usual practice although as' will be men tioned later this coil is preferably not ener- "z'ed strictly in accordance with a voltage.

he stabilizing relay devices C G are simi-' lar to the tripping devices and the corresponding coils are indicated with like index numerals. The energizing circuits for these coils will now be described.

Groups D D of three current transformers, having their secondaries star-connected on one side, are provided at the ends of the sections. Thus conveniently there are two groups D associated'respectively with tlie two sectionsA A and dis osed one on either side of the main circuitreaker A, whilst two further groups D also associated'one with each section are disposed between the power transformers A A and the line. The secondaries of the two groups of transformerseD'D associated with each section are connected to three summation transformers D, so that the secondary windings D" of the device B B" summation transformers a ply to the secondary circuits D E. M. F. s proportional to the total currents flowing in the respective "bases of the section at the adjacent end. he summat'ontransformer secondaries D, which are nnected in star on one side, are each connected on the other side through the current coils B C of the overload trippin and stabilizing relays B C in the correspon ing phase, the three secondary leads being star-connected on the other sides of the over- .lda drelays, The current coils B C of the earth leakage tripping and stabilizing relays B C are connected in series with'one another between the two star points of these e coils B C of the overload responding power transformer A A, suitable means indicated,at E bein provided for compensating for the volt op in the power transformer, so that the potential transformer secondary circuits will accurately reflect the voltage conditions -on the primary side of the transformer. In oriary switches (such interconnections being omitted from the drawings 1 for the sake Of simplicity) The voltage coils B C of the earth leakage relays 13 0 may be energized from a suitable potential s'ource, but preferably thesecoils are energized as shown in series from a current transformer F in the earthing connection A -to the neutral point of-the corresponding power transformer primary A. To provide for thecase when one power transformer is out of service, the two current transformer secondaries, F are connected to a summation transformer F whose second ary F supplies the voltage coils B C of the four earth leakage relays B 10 It will be apparent that since the operation of the earth leakage relays BPC? is entirely dependent onthe directionof'flow of the fault current in thecpower circuit and is independent (except for the limits imposed by the sensitiveness of the relays) of the magnitude of such current, the flow of current'through theneut'ral point earthing connection A will provide in a simple and economical manner a satisfactorybasis for comparison with the flow of total earth fault current in the section itself, and the arrangement is preferfault.

able to the use of? voltage element since it ensures correct discrimination even when there is a heavy fall in voltage due to the The contacts of the three overload tripping relays Band of the earth leakage trippingrelay B are connected in parallel with one another to control the energization from a local\D., C. source G of a tripping auxiliary relay H, and the contacts of the overload and earth leakage stabilizing relays C C similarly control a stabilizing auxiliary relay. J.

The twosubstations at the end'sof the section A are connected together through pilot wires, which are normally employed for va- I'lOllS purposes such for example as tele phony or the transmission; of indicating or controlling or metering currents in a remote control system, andrthe number and nature of such pilot wires will depend on the uses to which they are normally applied. For

tween the two substations, are normally em-' the purposes of the protective arrangement of Figures 1 and 2 three of these. pilotrwires G Gr Gr are required apd, for convenience of description, it will be assumed that two of these pilot wires G G which extend beploy'ed for telephonic purposes, (the telephone apparatus being indicated at G") whilst the'third is a return pilot extending continuously from station to station and may for instance form part of another telemain circuit-breaker A and for the circuitbrealger A? arranged between' the corresponding power transformer and the line; a

The other contactsH are arranged in the form of change-over contacts which nor. mally connect one; of the ilot wires G to .the telephone apparatus 4 but on operation of the relay connect that pilot wire through a lock-out relay K to the common return pilot G The normally closed contacts, K of the lock-out relay K? control-the circuit to the time-lag relay K, so that when the local battery 9 at the other substation is applied across these two pilot wires G G the look-out relay'li will. operate to deenergize the time-lag relay K and thus prevent tripping of the circuit-breakers A? A The contacts J of the stabilizing auxiliary'relay J are arranged as change-over contacts and serve to connect the remaining pilot wire G either to the telephone apparatus Gr or after operation of the relay to one pole of the local battery G,the other pole of which is permanently connected to the-common return pilot wire G. Thus the operation of the stabilizing auxiliary relay J will connect the local battery G across the two pilot wires G G across whlch the lock-out relay k at the remote end can be connected. h

The trippinrelay devices BB 1) b are so arrange at they. can only operate when the v is flowing into the section. A at the ad acent end, andjthe stabilizing relay devicesG C c 0 are arranged to operate only when the-current is fiowmg out of the section A at the 'adiacent end. I

Under normal conditions all the rela s are inoperative and the pilot {wires Gr 2 are connected to the telephone apparatus G g for use when required; If now a fault occurs at apoint external to the sec-' tion A under consideration, a. heavy current of relatively short duration Wlll flow throu h the section from end to end in one i directlon. This will cause the operation, of oneor more of the tripping relays B B at one end (namely that at which the our-- rent is entering the section) a and of-the cor responding stabilizing relays 1c 0 at .the. remote end of the section, the other relays remaining inoperative. The operation of tripping relays will also not operate, the the tripping auxiliary relayH at the first effect in such a case would be to trip out the end will complete the circuit to its time-lag] next section of the line, thereby effectively relay K and will disconnect-one pilot wire clearing the fault. Such a contingency is G? from the telephone apparatus G and however unlikel to occur, especially in the connect the lock-out relay K between this case of an over ead line system where the pilot wire Gr andithe common return pilot majority of faults would be earth faults.

wire G". At the other end of the section 1 In the event ofsimultaneous earth faults the operation of the stabilizin auxiliary on two sections of the line, the earth fault relayj will disconnectthe telep one appacurrents will in one faulty section flow in ratus g, from the same pilot wire Gr and the same direction at both ends whilst feed:

will connect the local battery 9 across the ing the second fault. The second faulty two pilot G G, thus energizing the section will however in-this case be cut out er 'ze the time-lag relay willconsequently complete their operation lock-out relay K at the first end. This in the normal manner, and the relays on the look-out relay K is thus 0 and the system both faults will be cleared. consequentl remaln stable. As soon The above arrangement may be modified as the fault is c eared, the relays will reset in various wa s. Thus if four pilot wires themselves and reestablish'the normal teleare available between two substations, one phone circuit. pair may be used for the transmission of If on the other hand a fault occurs in the stabilizing currents from one substation to section A itself, current will flow from both the lock-out relay at the second, whilst the ends of the; section inwards towards the stabilizin currents can be transmitted from fault; Thus the tripping overload or earth the secon leakage relays B B 1) 6 (according to at the first over the other pair of pilot wires. whether the fault is between phases or to, By'rearranging-the contacts on the auxiliary earth) at both ends of the section will be relays it is also possible to carry out the operated, whilst the stabilizing relays C C necessary operations with the use of two 0 c at both ends will remain inoperative.- pilot wires only, and such an arrangement The tripping auxiliary relays H h at both is illustrated in Figure 3 which shows a modends Wlll 0 rate then contacts and enerified form of the lower part of Figure 2 'ze their time-lag relays K k, \disconnect- (the same reference letters being employed in the telephone apparatus G g from the where applicable). pi ot wires Gr G and connecting the lock- In the arrangement of Figure 3 the tripout relays K 10 in circuit. Since however ping auxiliary relay H has three sets of neither stabilizing auxiliary rela J j is contacts H? H H, one H normally open operated, both lock-out relays wil remain. controlling the circuit to the time-lag tripdeenergized, and the time-lag relays K k in relay K as before and the other two l I TI in the form of change-over contacts and trip out the four circuit-breakers A 'which normally connect the two .pilot wires A a a at the ends of the section, the sup- G" G? to the contact arms J J of changeply to the two substations concerned, howover contacts on the stabilizing auxiliary 'eration of the earth leakage relays is ever, still being maintained through the relay J, but after operation of the tripping power transformers connected to the adjaauxiliary relay connect these pilot wires to cent healthy sections. The relays then reset the look-out relay K controlling the circuit substation to the look-out relay themselves to reestablish the normal teleto the time-lag relay K. The stabilizing 4 phone circuit. It will be, noticed that teleauxiliary relay chan e-over contacts J 2 J 3 phone communication over the pilot wires normally complete t e telephone or other G G is only 'interrufpted during the brief circuits but after operation of the relay'the period between the rst operatlon of the two contact arms are connected across the relays and the moment of clearing of the local battery G. Thus when a fault occurs fault, the time taken for clearin a fault external to the rotected section the stabilizbeing the same whatever the position of the ing auxiliary relay J at one end and the tripfault on the system.

Since, in the case of earth faults, the o ate,.so that in addition to the breaking o the etelephone circuits a circuit is established pendent on the flow. of fault current from the local batteryGat the stabilizin end :throu h the neutral point earthing connec over the pilot wires Gr G to the loc -out tions lnstead of on the Volta e, these relays relay k at the other end, the result being ,will operatewhatever the va ueof the voltthat the section is left in circuit atboth :age and correct discrimination will always ends. For aninternal fault neither stabilping auxiliary relay 7:. at the other end 0 erl'be Lobtained. In. the case of interphase izing auxiliary relay J j operates but both -falilts a heavy all in voltage may leave the tripping auxiliary relays H h operate so overload relays unaffected but sincethe stathat the feeder is cut out atboth ends.- bilizingrelays.adjacent to the inoperative Figure 4 shows a modification in which in the system irrespectitve of the direction similar to those of wires Gr G as before.

has three sets of contacts H 'cuits,these.contacts J J after operation of flow of current in the protected section. This arrangement is in many, respects identlcal with that of Figure 1 and the same reference letters are employed where applicable, the arrangement only being described in so far as it differs from that of Figure 1. The tripping and stabilizing relaydevices -B B 0 C1 are arranged as before, with the exception that the tripping relay devices B B no longer'haye directional properties and their voltage c'dils' B B are consequently omitted. Figure 4 shows certain small modifications in the energizing circuits'to the variousrelay coils (these modifications however beingequally a licable to the arrangement of Figure 1 hus the circuit-breaker A is itself inclu ed within the scope of the protection afforded to each section A A and consequently the current transformers D in each T-connected circuit cooperate with the current .transfor'mersD onthe remote side of the circuit-breaker A instead of with those on the near side. Again the summa tion transformers D are omitted,'tlie secondaries'of the transformers 'D I) being directly connected together and to the relay energizing conductors D". The summation transformer F is similarly omitted. The provisionof summation transformers .as in Figure 1 will however usually be desirable if the current transformers D andd) have different ratios or different secondary out-- uts. p Thecircuit.controlledby the tripping and stabilizing auxiliar relays H J are generally figure 3, the same reference letters being employed where applicable. Thus each tripping auxiliar relay H i H, of which the first H controls the circuit to the time-lag relay-K whilst the other two H H are arranged' as change-over. ontacts and normally connect up the .pilot wires G .Gr to form part of the telephone or other circuits (here shown as remote control circuits) but after operation connect the pilot wires to the look-out relay K These cir cuits however are in this arrangement also controlled by the stabilizing auxiliary relay 'J., This relay J has a further set of normally closed contacts J 2 which are in series with the contacts H and K in the energizing circuit to the time-lagrelay K, whilst itsfchange-over contacts J 3 J 4 normally complete the circuitto the lock-out relay K instead of the remote control or other cit.-

connecting the battery G across the, pilot Thus under normal conditions all the relays are inoperative-and the pilot wires are connected to form part of the remote control will flow through the section A from end .to"

end in one' direction. 'This will cause the operation bfone or more of the trippingrelays B B at both ends of-the section" and also of the correspondin stabilizing relays G C at the end at whic the fault current ,is flowing out from the feeder. The stabilizing auxiliary relay'J, at this end will break the circuit to the time-lagtripping relay K and thus prevent operation of the adjacent circuit-breakers A -A and will also connect its batter G over the pilot wires Gr- G through-the tacts H H of the trippin auxiliary relays H at both ends to the loc -0ut relay K at the other end, which breaks the circuitto the time-lag relay K at that end, this timelag relay havin started to operate when .80 change-over cdnthe tripping auxiliary relay H'had operated but being'locked out before its operation is completed. Thus the operation of the stabilizing auxiliary relay J at one end prevents opening of the circuit-breakers at both ends. The first operation of the two tripping auxiliary. relays H breaks the normal remote control circuit, but this circuit is reestablished bythe resettin of the relays as soon as the fault is clearer? If on the.other hand a fault occurs in the section A'itself, current will. flow from both ends -ofthe section inwards towards the fault. Thus the tripping overload or earth leakage relays B B (according to whether the fault is between phases or to earth) at both ends of the section will be operated, whilst the stabilizing relays C G at both ends will remain inoperative. The tripping auxiliary relays H at both ends will therefore break the remote control circuit and energize their time-lag relays K, the lockout relays K at the. two ends being connected together over a deenergized pilot circuit' and consequently remaining inopera-,

tive. The time-lag relays will thus complete their operation and trip out the-four circuit-breakers A -A at theends .of the section, the supply to the two substations concerned, however, bein g vmamtamed through the power. transformers connected to the two healthy sections. The relays then reset themselves to reestablish the normal remote control circuit, which has been interrupted only during the brief period between the first operation of the relays and the mo.-

ment oflclearing the fault, the time, taken for clearing a fault being the-same whatever the position of the fault on the system.

Withthis arrangement, as also in the preceding arrangements when forexample the pilot Wires are normally used for remote control purposes, it may be desirable in the 1 case when the remote control circuits carry 11C. currents to polarize oneor both of the lock-out relays in order to prevent'incorrect stabilization occurring as the result of operation of a lock-out relay by the remote control currents.

Figure 5 illustrates a modification of the above arrangements for the purpose of insuring satisfactory operation in the event of simultaneousearth faults on different phases of different sections of the network. In the previous arrangements there is risk of incorrect operation in such an event if it should happen that the two earth faults are fed in opposite directions through a part of the line intermediate between the faults, this operationoccurring as the result of the operation of the overload relays dealing with interphase faults. This disability can be overcome by utilizing the fact that under such unusual circumstances there is always a residual current suflic'ient to operate the earth leakage relays. Thus if the earth leakage relays are so arranged that when they operate they render the tripping overload relays ineffective, the desired result will be obtained. ()ne convenient arrangement to this end is shown in Figure 5 in which 'tl'iesupply to the tripping auxiliary relay H is controlled by both'earth leakage relays B C ,-but its operation from the overload relays Ii C is controlled by the normally closed contacts L of an auxiliary relay L, which is operated whenever either earth leakage relay B or C? operates. The stabilizing auxiliary relay J is' directly controlled as before by'the stabilizing overload and earth leakage relays C C. Thus an earth fault automatically takes precedence over an inter-phase fault and correct operation is insured.

In the arrangements above described, the

. natln when there is no neutral point earthing connection available, this arrangement being illustrated by way of example in its application to the arrangement of Figure 4, the same reference letters being employed where applicable.

In the arrangement of Figure 6, the voltage coil 0 is energized from the 1)en-delta-connected secondary F of an auxiliary potential transformer whose primary F is supplied from the secondary E of the main potential transformer rom which the voltage coils C? of the intcrphase fault ovcrload directional relays C are energized, this main potential transformer being connected up in the well-known manner. \Vith this arrangement it will be appreciated that the earth leakage voltage coils C auxiliariy frequency currents su arrangement of Figure 1, in which case the ary F will supply the voltage coils B secon C oflthe tripping and stabilizing earth leakage relays B (J in series.

Figure 7 shows another modification of the energizing circuits 'of the overload relays. Under certain circumstances of light load on a ower system. the short-circuit current on ault is limited to a value below the normal full-load value, and Figure 7 shows a convenient arrangement for ensur- .ing operation of the overload relays (say,

the relays C) under such conditions but yet preventin operation under normal fullload conditions. ating coil of anon-directions. overload relay or (as shown) the current coil (L of a directional overload relay C is under normal full-load conditions short-circuited by the contacts M M of an auxiliary overload relay M and of an auxiliary low-volt rela M, and the operation of the relay C will t erefore be dependent upon the setting of the overload relay M. If the voltage falls be ow, a predetermined value the .aux-

"iliary low-volt relay M opens its contacts M and thus renders the relay C o rative. The relay C is thus put into circuit either on excessive riseof current or on excessive fall of voltage. In effect this is equivalent to providin the relay C with two settings, the choice 0 which is determined in accordance with the voltage conditions.

The above arran ements may be modified in various ways. bus for instance alterma e transmitted over the pilot wires for sta ilizing purposes, or pilot wires ma be dispensed with altogetherby the use of high 'rimposed'on one or more of the power con uctors. One convencurrents instead of direct currents For this purpose the oper- I ient superimposed current arran ement is illustrated by way of example in igure 8, the arrangement shown being analogous to that of Figure 4. s

In the arrangement of Figure 8 the tripping and stabilizing relay3 device's (diagrammatlcally indicate at 'and C) are arranged as in Figure 4 and control the tripping and stabillzin auxiliary relays H J.

'The stabilizing auxiliar rela acts at contacts J to connect up a igh requency generator-indicated at N, so that it can transmit high frequency currents through 'suitable coupling devices over one or more ofthe ceiver indicated at N which is connected up by the operatlon of the contacts H of the tripping auxiliary relay H. The time-de layrelay K is as before. controlled by the contacts J H K of the stabilizing auxiliary relay J, the trippiig auxiliary relay tion is to the discriminate protection over two pilot wires of duplicate feeders. Figure 9 shows. a convenient arrangement to this end, which will be described by way of example with reference to the arrangement of Figure 4. In this arrangement each of the twofee'ders O0. is provided with tripping and stabilizing relay devices P Q, or R S controlling auxiliary relays R S and P Q respectively and the desired discrimination is obtainedby varying the amount of sta- 'bilizing current allowed to flow through the look-out relays, of which three T T T are employed in series in place of each lock-out relay inthe previous arrangements. The three lock out relays have different current settings, for example, in the proportion of 1: 2:4. The -first lock-out relay T with the lowest setting stabilizes the first feeder O by breaking at contacts T the circuit to the time-lag relay 0 associated with the feeder O. "The second lock-out relay T with the ,intermediate setting stabilizes the second feeder O by breaking at contacts T the circuit to the time lag relay 0 of the second feeder O and also remakes at contacts T the the time-la'g relay 0 leaving the circuit to the time-lag relay 0 broken by the second lock-out relay at contacts T The tripping auxiliary relays P R each have five sets of contacts.

- and the other pilot wire '0 is similarly connected in its normal circuit by the contacts P- R. The normallyopen contacts P and B respectively control the energizing circuits of the time-lag relays O and O and the remaining'normally open contacts 1? R P R control the connections of the pilot Wires 0 0" to contacts on the stabilizing auxiliary relays Q, S, each of which has six sets of contacts. The normally closed con tacts Q," and S respectively control the circuitsrto the time-lag relays O and O and the normally closed contacts Q Q S control the connections from the pilot wires 0* O to the look-out rclaysT T T through The normally closed contacts P 11 in series control, the

the contaets I R P R. The normally open contacts Q," S control a direct connection throughthe contacts P R from the pilot wire ()to one pole of the local battery O, the other pole of which is connected through a graded limiting resistance 0 .to

operation of one or both stabilizing relays ensures the. operation of the appropriate lock-out relay at the remote end, so that if a fault occurs on one feeder-the faulty feeder is.cut out and the healthy feeder left in circuit whilst if the fault is external to the feeders both feeders are left in circuit.

This arrangement may be modified in various ways, forexample by obtaining discriminative operation of the look-out relays ;by means of two equal D. C. currents of op- ,posite polarity and a third current of different magnitude or by means of threeA. C. currents of different frequencies.

These arrangements have an advantage over known protective arrangements for duplicate feeders, in that they are operative Whether the two feeders are connected in parallel or not. Indeed the feeders maybe entirely independent of one another and may even carry different voltages. Thesev arrangements however fail to operate satisfactorilyin the unusual event of the two feeders being connected up in series with one an other so as to constitutea eonnection between two busbar sections in the same station. This disability lean however be overcome by .i employing three pllot. wires instead of two, so that each feeder is protectedby onepilot wire and a common returnpilot Wire, or in other ways. a

The arrangement may also be" extended to deal with the'case of duplicate feeders, one of Which is broken at one or mere points for supply tointermediate substations.

Such anarraiigement is shown in-Figure 10 for the case of two feeders, one of which U extends between two stations V and W whilst the other U U is broken" at a single intermediate station Three pilot 'wires are employed, onc of which U serves as a Whilst the third is formed in two parts U U respectively cooperating with the return pilot U for stabilizing the parts UFU of" the broken feeder. In the example illusdelay trated, these pilot wires are shown as normally employed for telephonic purposes, the telephone apparatus being indlcated at V W X Each station has a localbatter V or W or X, the connections being such that the direction of stabilizingcurrentfiow in the return pilot Uis the same for all cases. For the protection of the feeder U,

the station v'isprovided with a tripping tion U The manner of operation of these relays will be clear without further description from the descriptions of the other arrangements above given, the circuits actually shown being similar tothose of Figure 4...

The arrangements above described may be modified where necessary to suit the type of circuit to be protected. Thus for example the arrangement may be applied with slight modification to the protection of a section between two substations of the kind in which the incoming and outgoing sections are connected to one or more sets of busbars,

to which any desired number of power transformers or other apparatus can be connected. The invention may also be applied to the protection of busbars or of electrical apparatus, such as transformers or motor generators or other'machines, For the protection of D. C; circuits or apparatus polarized tripping andstabilizing relays either directly connected in the protected circuit or energized from shunts therein may be employed, the eneral arrangement of such relays dependlng on the nature of the circuit to be protected.

What we claim as our invention and desire to secure Letters Patent is 1. The combination with a sectionalized" ele'ctric powercircuit, of circuit-breakers for isolating the sections of the power circuit from one another, a tripping circuit for each circuit-breaker, and means for protecting each section independently of the other sections comprising a tripping relay device at I each end controlling the tripping circuit for the ad'acent circuit-breaker, a stabilizing relay evice at each end 0 erative' on the occurrence of a fault on t e system only when the current ip the power circuit is flowing out from the section at the'end adjacent to the stabilizing relay device, means whereby each stabilizing relay device when operated causes a stabilizing current to be opened by its tripping rela device.

transmitted to the remoteend of the section and means at each end operated by the stabilizing current from'the remote end to prevent the adjacent circuit-breaker from being 2. The combination wit a sectionalized electric power. circuit, of circuit-breakers for isolating the sections of the power circuit from one another, a tripping circuit for each circuit-breaker, and means for protecting each section independently of the other sections comprisin a tripping relay device at each end controlling the tripping circuit for the adjacent circuit-breaker and operative on the occurrence of a fault in the system irrespective of the direction of current flow in t e protected section, a stabilizing relay device at each end operative on the occurrence ofa fault on the system'onl when the current in the power circuit is owing out from the section at the end adjacent to the stabilizing relay device, means whereby each stabilizing relay device when operated causes a stabilizing currentto be transmitted to the remote end of the section and means at each end operated b the stabilizing current from the remote en to prevent the adjacent circhit-breaker from being opened by its tripping relay device.

- 3. The combination with a sectionalized electric power circuit, of circuit-breakers for isolating the sections. of the power circuit from one another, a tripping circuit for each circuit-breaker, and means for protecting each section independently of the other sections comprising a tripping relay device at each end controlling the tripping circuit for the adjacent circuit-breaker and operative on the occurrence of a fault in the system irrespective of the direction of current flow in the protected section, a stabilizing relay device at each endoperative on the occurrence of a fault-in the system only when the current in the power circuit is owing out from the section at the end adjacent to the stabilizing relay device, means whereby each stabilizing relay device when operated acts to prevent the adjacent circuit-breaker from being opened by its tripping relay device and to cause a stabilizing current to a transmitted to the remote end of the section and means at each end operated by the Slilblllb ing current from the remote end to prevent the adjacent circuit-breaker from being opened by its tripping relay device.

4. The combination with a sectionalized electric power circuit, of circuit-breakers for isolating the sections of the power circuit from one another, a tripping circuit for each circuit-breaker, and means for protecting each section independently of the other sections comprising a tripping relay device at each end controlling the tripping circuit for the adjacent cireuit breaker, a stabilizing 1ev device at each end operative on the occurthe stabilizing relay device, a lock-out relay from one another, a tripping circuit for each at each end acting when operated to prevent the adjacent circuit-breaker from being opened by its triplping relaydevice, and means whereby eac stabilizing relay device when operated causes a stabilizing current to be transmitted to the remote end of the section for the operation of the lookout relay at that end. i

5. The combination with a sectionalized electric power circuit, of circuit-breakers for from one another,a tripping circuit for each circuit-breaker, and means for protecting each section independently of the other sections comprising a time-lag relay at each end controlling the tripping circuit for the adjacent circuit-breaker, a tripping relay device at each end operative to energize the adjacent time lag relay on the occurrence of a fault on the system irrespective of the direction of current flow in the protected section, a lock-out relay at each end acting when operated to 'breakthe energizing circuit to the adjacent time-lag relay, a stabilizing relay device at each end operative isolating the sections of the power circuit on the occurrence of a fault in the system circuit-breaker, and means for protecting each section independently of the other sections comprising a tripping relay device at each end controlling the tripping circuit for the adjacent circuit-breaker and operative on the occurrence of a fault in the system' irrespective of the direction of current flow in the protected section, a lock-out relay at each end acting when operated to prevent the adjacent circuit-breaker frombeing opened by its tripping relay device, a stabilizing relay device at each end operative on the occurrence of a fault in the system only when the current in the power circuit is flowing out from the section at the end adjacent to thestabilizing relay device, and means whereby each stabilizing relay device when operated acts to prevent the adjacent circuit-breaker from being opened by its tripping relay device and causes a stabilizing current to be transmitted to the remote endof the sectionfor the operation of the lockout relay at that end. s '6. The combination with a sectionalized electric power circuit, of circuit-breakers for isolating the sections of the power circuit from one another, a tripping circuit for each circuit-breaker, and means for protect ing each section independently of the other sections comprising a time-lag relay at each end controlling the tripping circuit for the adjacent circuit-breaker, means operative on theoccurrence of a, fault on the system for energizing the time-lag relays, a lock-out relay at each end acting when operated to break the energizing. circuit to the adjacent time-lag relay, a stabilizing relay device at each end operative on the occurrence of a only when the current in the power circuit is flowing out-from the section at the end electric power circuit, of circuit-breakers for isolating the sections of the power circuit from one another, a tripping circuit for each circuit-breaker, and means vfor protecting each section independently of the other sections comprising pilot wires extending from one end of thesection to the other, a local source of current at each end, a tripping relay device at each end controlling the tripping circuit for the adjacent circuit-breaker, a lock-out relay at each end acting when operated to prevent the adjacent circuitbreaker from being opened by its tripping relay device, a stabilizing relay device at each'end operative on the occurrence of a fault on the system only when the current in the power circuit is flowing out from the section at the end adjacent to the stabilizing relay device, and means whereby each stabilizing'relay device when operated acts toconnect the adjacent source of current to the pilot wires for the energization of the look-out relay at the remote end. i

9. The combination with a sectionalized electric power circuit, of circuit-breakers for isolating the sections of the power circuit from oneanother, a tripping circuit for each circuit-breaker, and means for protecting each section independently of theother sections comprising pilot wires extending from one end of the section to the other, a local source of current at each end, a tripping relay device at each end controllin thetripping circuit for the adjacent circu1t-breaker and operative on the occurrence of a fault on the system irrespective of the direction of current flow in the protected section, a lock-out relay at each end acting when operated to prevent the adjacent circuitand also to connect the adjacent source of current tothe pilot wires for the energization of the lock-out relay at the remote end.

10. The combination with a sectionalized electric power circuit, of circuit-breakers for isolating the sections of the power circuit from one another, a tripping circuit for each circuit-breaker, and means for protecting each section independently of the other sections comprising pilot wires extending from one end of the section to the other, a local sourceof current at each end, a'time-lag relay at each end controlling the tripping circuit for the adjacent circuit-breaker, means operative on the'occurrence of a fault on the system for energizing the time-lag relays, a lock-out relay at each end acting when operated to break the energizing circuit to the adjacenttime-lag relay, a stabilizing relay device at each end operative on the occurrence of a fault in the system only when the current in the power circuit is flowing out from the section at the end adjacent to the stabilizin relay device, and means whereb each sta ilizin relay device vwhen operated 1 acts to break t e energizing circuit to the adjacent time-lag relay and to connect the adjacent source of current to the pilot wires for the energization ofathe lockout relay at the remote end.

' 11. The combination with .a' sectionali'zed electric power circuit, of circuit-breakersvfdr isolating the sections of the power circuit from. one another, a tripping circuit for each circuit-breaker, and means forprotecting each section independently of the other sections comprising pilot wires extending from one end of the section to the other and normally being utilized for purposesother than protective urposes a tri ping relay device at each en controlling t etnpping circuit for the adj acent circuit-breaker, a stabilizing relay device at each end operative .on the occurrence of a fault on thesystem onl when the current in the power circuit is owing out from the section at the end adjacent to the stabilizing rela device, means operative on the occurrence 0 a fault on the system for transferring the connections of the pilot wires from theirnormal condition into a condition in which theycan be utilized for thetransmission of stabilizing currents,

, means whereb -each stabilizing whem oper causes a stabi izing current to be transmitted to the remote end and relay device) means at each end operated b the stabilizing current from the remote en to prevent the adjacent circuit-breaker from being opened by its tripping relay device.

12. The combination with a sectiOnalized electric power circuit, of circuit-breakers for isolating the sections of the power circuit from one another, a tripping circuit for each circuit-breaker, and meansfor protecting each section independently of the other sections comprisin two pilot wires extendin from one end 0 the section to the other an normally being utilized for urposes other than protectiie purposes, a ocal source of current at each end at each end controlling t e tripping circuit for the adjacent circuit-breaker and operative on the occurrence of a fault in the system irrespective of the direction of current flow in the-protected section, a lock-out relay at each end acting when operated to prevent the ad'acent circuit-breaker 'from being opened y its tripping relay device, a stabilizing relay device at each end operative on the occurrence of a fault in the system only when the currentin the power circuit is flowin out from the protected section at the end a jacent to the stabilizing relaydevice, means whereby the tripping ,relay devices .act when operated to disconnect the pilot wires from their normal connections and to connect them to the lock-out relays, and means whereby either stabilizing relay device whenoperated acts to prevent the adjacent circuit-breaker from being opened by its tripping relay device and also to transfer the connections of the pilot wires from the adjacent lock-out relay to the adjacent source of current whereby the lock-out relay atthe remote end is operated.

13. The combination with a sectionalized electric power circuit,'of circuit-breakers for isolating the sections of the power circuit from one another, a tripping circuit for each circuit-breaker, and means for protecting each section independently of the other sections comprising a tripping relay device at each end consisting of an earth-leakage relay and at least one overload relaysuch device being operative on the occurrence of an earth or interphase" fault on the system to control the tri ping circuit for the adjacent. circuit-mea er; a stabilizing relay device at' each end operative on the occurrence of a fault on the system only whenothe current in the power circuit is flowing out from the section at the end adjacent to the a tri ping relay device stabilizing rela device, means whereby each fstabilizingl re ay device when operatedcauses a stabilizing current to be transmitted to the remote end ofthe section and meansat each end operated b the stabilizing current from the remote en to prevent the adjacent circuit-breaker from being opened by its tripping relay device.

14. The combination with a sectionalized electric power circuit, of circuit-breakers for isolating the sections of the power circuit from one another, a tripping circuit for each circuit-breaker, and means for protecting each section independently of the other sections comprising a tripping relay device at each end consisting of an earth-leakage relay and at least one overload relay such tripping relay device being operative on the of the section for the operation of the lockout relay at'that end.

In testimony whereof we have signed our names to-this specification.

ERIC WALTER MARBURY SCOTT.

BRUCE HAMER LEESON.

. adjacent to the stabilizing relay device, and v means whereby each stabilizing relay device when operated acts to prevent the circuitbreakers at both ends of the section from being opened by their tripping relay devices.

15. The combination with a sectionalized electric power circuit, of circuit-breakers for isolating the sections of the power circuit from one another, a tripping circuit for each circuit-breaker, and means for protecting each section independently of the other sections comprising a time-lag relay at each end controlling the tripping circuit for the adjacent circuit-breaker, a tripping relay device at each end consisting of an earth-leakage relay .and at least one overload relay such tripping relay device being operative on the occurrence of an earth or i-nterphasefault on the system irrespective of the direction of current flow in the protected section, a tripping auxiliary relay'at each end which is energized by the operation of any one of the relays of the adjacent tripping relay device and acts to energize the adjacent timelag relay, a lock-out relay at each end acting when operated to break the energizing circuit to the adjacent time-lag relay, a stabilizing relay device at each end consisting of a directional earth-leakage relay and at least one directional overload relay such stabilizing relay, device being operative on the occurrence of an earth or interphase fault in the system only when the fault current in the power circuit is flowing out from the pro-' tected section at the'end adjacent to the stabilizing relay device, anda stabilizing aux- 'iliary relay at each end which is energized by the operation of any one of the relays of the adjacent stabilizing relay device and acts f to break theenergizing circuit to the adjacent time-lag relay and to cause a stabilizing current to transmitted to the remote end 

